Human intracranial nerve tissue includes regions that are stimulated by optical radiation directed at the regions. Stimulation may have a metabolic and/or nervous response, which appears as a change in alertness, diurnal rhythm and in concentrations of several hormones and brain transmitters. At the moment, phenomena known to be caused by changes in the amount of light include onset of copulation behaviour in wild animals and well-known seasonal affective disorder (SAD) in humans. Optical radiation may originate from nature, or optical radiation may have an artificial origin.
It is typically necessary to use artificial optical radiation when natural light is not sufficient for achieving a desired physiological effect. Artificial optical radiation may also be generated by bright light therapy devices installed in homes or workplaces, for instance.
A disadvantage of bright light therapy devices is that they are large, are restricted to a certain place, have a poor efficiency and cause disturbance to the environment. Consequently, it is useful to consider alternative techniques for achieving interaction between optical radiation and intracranial nerve tissue.